It requires you to do a lot of things differently design wise, specifically It breaks particle effects and lighting. If you still want to do it then all you need is a simple vertex shader to adjust the world position of vertices based on a spherical projection. Basically you take the world position of every vertex position and pass it to a function that calculates a custom perspective projection.

I need this, how did you do this, im making a 3D bullet hell and this would probably be good for it